Heretofore, polyethylenepolyamine compounds such as diethylenetriamine, triethylenetetramine and the higher homologs have been produced by the reaction of an alkyl halide such as ethylene dichloride with an amine such as ammonia or ethylenediamine at elevated temperatures and pressures. Normally, relatively high yields of predominantly non-cyclic polyethylenepolyamine compounds are obtained from this process with varying yields of heterocyclic amines. The large amounts of energy required to produce the reactants as well as the difficult separation procedures required to recover the more valuable linear polyethylenepolyamines diminish the usefulness of the ethylene dichloride process. The hydrohalide salts of ammonia and the polyethylenepolyamine products must also undergo difficult and time consuming caustic neutralization to yield the free polyethylenepolyamines.
The production of polyethylenepolyamines from the starting reactants of an alkyleneamine and an alkanolamine is a process that has come under recent research scrutiny. Two feasible reactants for this process in terms of cost and availability are ethylenediamine and monoethanolamine. Unfortunately, reaction of these two reagents tends to produces copious quantities of cyclic products diminishing the possible yield of the more valuable and sought after linear polyethylenepolyamines.
When catalyzed, the reaction of monoethanolamine and ethylenediamine yields numerous products. The most desirable products are the predominantly linear polyethylenepolyamines. Products that are less desirable include such cyclic compounds as:
AEP--N-(2-aminoethyl)piperazine PA1 DiAEP--diaminoethylpiperazine PA1 PEEDA--piperazinoethylethylenediamine
It is believed that this propensity to create myriad products is due to the primary amine nature of both monoethanolamine and ethylenediamine, which offer considerably more reactive hydrogen sites and product possibilities than tertiary or secondary amines.
It is well known that different classes of amines--primary, secondary and tertiary--generally react in different ways. In many reactions, the final products depend upon the number of hydrogen atoms attached to the nitrogen atom, and hence are different for amines of different classes. See, R. Morrison and R. Boyd, Organic Chemistry, Allyn and Bacon, Inc., New York (3rd ed. 1973) p. 728. Chemists have taken advantage of the differences in reaction between amine classes to develop several tests for distinguishing between primary, secondary and tertiary amines; most notably, the isocyanide test for primary amines, enamine formation from aldehydes and ketones for secondary amines, the Hinsberg reaction, hydrogen peroxide or peracid reactions, and nitrous acid reactions with all three classes of amines. See, Kirk-Othmer Encyclopedia of Chemical Technology, John Wiley & Sons, New York (3rd ed. 1978) Vol. 2, pp. 272, 275 and C. Noller, Chemistry of Organic Compounds, W. B. Saunders Co., Philadelphia (3rd ed. 1965) pp. 260,509.
U.S. Pat. No. 4,044,053 discloses a process for preparing polyalkylenepolyamines from an alkyleneamine and ethylene glycol in the presence of a phosphorus-containing compound. However, neither the unique aluminum phosphate catalyst of the claimed invention, nor the surprising results achieved thereby, is disclosed in said patent. U.S. Pat. No. 4,036,881 discloses a method of reacting an alkyleneamine with an alkanolamine in the presence of a phosphorus-containing compound of the group consisting of acidic metal phosphates, phosphoric acid compounds and alkyl or aryl phosphate esters. Although aluminum phosphate is mentioned as a catalyst, it is not the aluminum phosphate catalyst prepared in accordance with the invention. The process of '881 yields a relatively lower conversion to linear polyethylenepolyamines when the disclosed catalyst is employed, rather than the catalyst prepared according to the present invention.
Aluminum phosphate has been thought to be a compound which would catalyze reactions to produce predominantly heterocyclic rather than linear products. U.S. Pat. No. 3,297,701 teaches using aluminum phosphate to catalyze ethanolamines and polyethylenepolyamines to yield cyclic compounds. U.S. Pat. No. 3,342,820 also discloses the use of an aluminum phosphate catalyst for the preparation of heterocyclic compounds such as triethylenediamine.
U.S. Pat. No. 4,103,087 issued to Brennan provides a third example of an aluminum phosphate catalyst for producing heterocyclic product compounds. This Brennan patent discloses a process for making a di-(N,N-disubstituted amino) alkane compound containing a morpholine substituent from a tertiary aminoalkanol and a secondary amine. Because the Brennan reference reacts a tertiary amine with a secondary amine, the reactions and products are relatively simple compared with the numerous additional reactions and myriad byproducts created when two primary amines are reacted according to the present invention. Indeed, the Brennan reference does not discuss at all the subject of the present invention, the preparation of linear polyethylenepolyamines. It is instead concerned with the preparation of morpholine compounds. Thus, it would be difficult to predict the numerous byproducts formed from the reaction of two primary amines from knowledge of the reaction between a tertiary and a secondary amine having different compositions. At best, a survey of the prior art would lead a skilled chemist to the conclusion that aluminum phosphate compounds employed as catalysts yield predominantly heterocyclic products.